1. Field of the Invention
This invention relates to a thermoplastic resin composition comprising a propylene-ethylene block copolymer resin, a low crystalline ethylene-octene copolymer, a low crystalline ethylene-butene copolymer, a specific elastomer having a block structure, talc, and a specific additive admixture, which is excellent in terms of processability on injection molding and in the appearance of a molded product, has good flexural modulus, impact resistance, elongation in tension, surface hardness, and heat resistance, and is also excellent in adhesion to a paint film and improved in terms of prevention of mold contamination, and thus is particularly suited for the production of injection-molded products such as automotive interior trims.
2. Background Art
So far, numerous attempts have been made to increase the impact resistance and rigidity of polypropylene resins by the addition thereto of ethylene-propylene copolymers, various ethylene copolymers, and talc. For instance, resin compositions having excellent impact resistance are known from JP-B-63-42929, JP-A-64-150, JP-A-64-66263, and JP-A-1-204946.
However, the composition set forth in the above JP-B-63-42929 is insufficient in flexural modulus and heat resistance due to the use of a polypropylene of not so high crystallinity.
The compositions described in JP-A-64-150, JP-A-64-66263 and JP-A-1-204946, because of their low talc content, are suited for some applications, e.g., bumpers but their flexural modulus is too low for interior trims.
Furthermore, JP-A-4-159345 discloses an ethylene-.alpha.-olefin copolymer composition containing a large amount of inorganic filler. This composition has a high specific gravity, and thus is not preferred in the light of weight reduction of automobiles.
In order to reduce the above drawbacks, JP-A-7-53843 has proposed a composition. This composition, however, is unsatisfactory in fluidity for use in applications requiring a higher level of fluidity where molding should be carried out at a low pressure in short cycle times.
Regarding the interior trims, they are in most cases coated with a paint to enhance the commercial value. Unfortunately, however, polypropylene materials for interior trims generally exhibit poor adhesion to a paint film, especially when fats and oils are involved. Therefore, the development of materials having higher adhesion to a paint film has been desired in the art.
On the other hand, there is the following problem with the conventional talc-containing polypropylene composite materials at the time of their molding. Thus, during the long-term continuous molding of the composite materials, bleedouts are gradually deposited on molds, whereby the resulting molded product undesirably exhibits a high gloss. This is particularly pointed out for automotive interior trims. A propylene polymer which provides a solution to this problem while maintaining the physical properties has been proposed in JP-A-5-209094 and JP-A-6-17982. However, this polymer utilizes no weathering agent. In view of the fact that stabilizers used for improving weathering resistance usually exert an adverse influence on the contamination of molds, there is still left much to be desired.
An object of the present invention is to provide a thermoplastic resin composition which has high fluidity, good physical properties and excellent moldability, can provide moldings having good adhesion to a paint film, is improved in terms of prevention of mold contamination, and is especially suited for the production of automotive interior trims such as an instrument panel.